"I am completely confident that Sweden will become a full member of NATO," Stoltenberg said in Oslo during an informal meeting of NATO's foreign ministers on Wednesday and Thursday.

Turkey and Hungary are the only countries of NATO's 31 member states that have yet to ratify Sweden's membership.

Finland formally became the Alliance's 31st member on April 4.

The two Nordic countries both dropped decades of military non-alignment and applied for membership together in the wake of Russia's invasion of Ukraine.

Erdogan, who was re-elected Sunday for another five-year-term, has accused Sweden of being a haven for "terrorists", especially members of the Kurdistan Workers' Party (PKK).

"We will be in close contact with Ankara and President Erdogan to help this process move forward as quickly as possible", Stoltenberg told reporters after Tuesday's discussion.

"They have already come an extremely long way since all the member countries, including Turkey, invited them to become full members at the summit last year", he added, referring to a Madrid summit in June.

Since the summit, Erdogan has also accused Sweden of not honouring the terms of a separate deal under which Turkey had agreed to approve the bids.

"I have been of the opinion since last autumn that Sweden should already have been admitted by ratification, and I am still of that opinion, but when 31 countries have to agree, it probably takes a little longer than I would like, so we are working on it", Stoltenberg said.

On Tuesday, Sweden once again drew Turkish ire, as Turkey deplored an "unacceptable" protest by Swedish activists aimed at Ankara.

The pro-Kurdish Rojava Committee of Sweden posted an anti-Erdogan video on social networks on Monday showing a PKK flag being projected onto the Swedish parliament -- the latest of several similar stunts by the group which has repeatedly provoked Ankara.

Although Turkey's foreign minister is not scheduled to be present in Oslo this week, the question of Sweden's candidacy will probably be raised again at an upcoming summit in Vilnius on July 11 and 12.